M66.321 Spontaneous rupture of flexor tendons, right upper arm

Billable ICD-10-CM code, FY2026.

Applies from M66 Spontaneous rupture of synovium and tendon

Includes

• rupture that occurs when a normal force is applied to tissues that are inferred to have less than normal strength

Excludes2 (not included here)

• rotator cuff syndrome (M75.1-)
• rupture where an abnormal force is applied to normal tissue - see injury of tendon by body region

MS-DRG index

Defines the logic of DRG(s) 557-558 in MDC 08.

Approximate ICD-9-CM (GEMs)

• 727.62 Nontraumatic rupture of tendons of biceps (long head) (approximate)

Code annotations containing back-references to M66.321

Back-references to M66

• Type 2 Excludes: M62.1 Other rupture of muscle (nontraumatic) ("rupture of tendon (M66.-)")

Nearby codes

• M66.31 Spontaneous rupture of flexor tendons, shoulder
• M66.311 Spontaneous rupture of flexor tendons, right shoulder
• M66.312 Spontaneous rupture of flexor tendons, left shoulder
• M66.319 Spontaneous rupture of flexor tendons, unspecified shoulder
• M66.32 Spontaneous rupture of flexor tendons, upper arm
• M66.321 Spontaneous rupture of flexor tendons, right upper arm (this code)
• M66.322 Spontaneous rupture of flexor tendons, left upper arm
• M66.329 Spontaneous rupture of flexor tendons, unspecified upper arm
• M66.33 Spontaneous rupture of flexor tendons, forearm
• M66.331 Spontaneous rupture of flexor tendons, right forearm
• M66.332 Spontaneous rupture of flexor tendons, left forearm